In the applications of lasers to isotope enrichment, particularly uranium enrichment as represented in U.S. Pat. Nos. 3,772,519 and 3,944,947. Very high repetition rate pulsed lasers are desired in order to increase the processing rate in which isotopes may be separated. To achieve high repetition rate laser pulses requires among other things high pulse rate flashlamps for excitation of the lasing medium, typically a flowing dye solution in this application. While pulse rates of substantially over a 100 pulses per second may be achieved with conventional flashlamps, rates approaching or exceeding 1,000 pulses per second result in a substantial elongation of the pulse duration which destroys the high pulse rate performance. The pulse elongation which occurs at high pulse rates appears to be due to the accumulation of energy within the discharged gas beyond that which is exhausted by radiation or conduction the accumulation being aggrevated at high pulse rate due to the increase energy applied to the gas by the more frequent application of electrical discharge potentials to the flashlamp electrodes.